I am trying to piece a Jacob's ladder and the first block has not come out square. The instructions I have are using a method I have not tried before...they call it a "sandwich method for doing the triangle where you cut two 4 7/8 inch squares, mark a center line from corner to corner and sew a quarter inch on each side of the line and then cut it in half. For the 4 blocks, you sew two strips 2 1/2 inches wide together, then cut those up into 2 1/2 inch sections and sew again to make the 4 piece block. When I sewed all the pieces together for the block I found that I needed to really stretch the two blocks to match up with the edges of the triangles and then when I got the first block done it was still out of whack. I have remeasured my cutting and it is good and also measured the seams and they are 1/4 inch. Do I need to do a scant 1/4 inch for this block or do you have another suggestion? Thanks
The finished block is "supposed" to measure 12 1/2 square. As you can see, my sides measure anywhere from 12 to 12 1/2 inches.

Did each of those blocks measure 4.5" BEFORE you put them together?

My guess is it's the HST block that was a bit small.

Try the method again, but this time start with 5.25" squares.
Make the diagonal line, sew on each side, cut and press.
NOW trim it down to 4.5" square.

I always use this "cut big and trim down" method. It results in a perfect square each and every time.
4-7/8" is exact...if you're off the slightest bit while cutting or sewing, you're never going to get the correct UNFINISHED size.

Did you square up the 4-patches and the HST after making each unit? That may be the problem if you didn't. They should each square up to 4 1/2". I've made HST & 4-patches before using those methods (but taking care to square the units) and haven't had a problem. Also, are you sure you're using a 1/4" seam allowance?

FYI -
The exact formula for calculating the starting squares for HST blocks is:
FINISHED size of the block plus 7/8"

So by adding 1" or 1.25" you're giving yourself a bit of wiggle room. And then it's easy to trim down to the UNFINISHED size.

Im thinking that its just from pressing. Looks to me like its just stretched a bit. Make another one that its suppose to attach to and see if your seams line up. Let me know.
That stretching thing can throw ya off and you wont realize it.
Good luck!!

I do this technique a lot and I love it. My guess is that your squares that you picked up were 4.5 rather than 4 7/8 or that your 1/4 inch was not scant enough. I always sew a little to the inside of the drawn line (toward the center diagonal). Good luck

I agree with MTS, I prefer to trim down. No one likes to square, but I love it now. Only because I have learned over the years, that you will regret it later.

I love your fabric choices. Good Luck, hang in there.

Cut big and square down is my method too! Also using a scant 1/4 inch.

Good Luck1

GREAT ADVICE MTS !!! There are so many times that you can CUT BIG AND TRIM. I do it ALL the time. REMEMBER that when you press a seam allowance, you always loose a tiny bit of fabric due to the bulk. With this technique, you don't have to worry about THAT problem. GOOD LUCK !!! :mrgreen:

Just as an aside, I see you are using a June Tailor cushioned mat to measure. Have you checked it to make sure it's accurate? The only reason I ask is because I had one (smaller) and it was NOT square. :(